A rate "lock" or "commitment" is a lender's promise to freeze a particular interest rate and a specific number of points for you for a specified period of time while your application is processed. This keeps you from going through your whole application process and discovering at the end that the interest rate has risen higher.
Although there might be a choice of rate lock periods (from 15 to 60 days), the extended ones are generally more expensive. A lending institution will agree to freeze an interest rate and points for a longer period, like sixty days, but in exchange, the rate (and sometimes points) will be higher than that of a rate lock of a shorter period.
There are more ways to get a good rate, besides opting for a shorter rate lock period. The bigger the down payment, the smaller your interest rate will be, as you will have more equity from the beginning. You can pay points to lower your interest rate over the life of the loan, meaning you pay more initially. One strategy that is a good option for some is to pay points to improve the interest rate over the term of the loan. You will pay more initially, but you will come out ahead in the end.
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